1. Field of the Invention
The present invention relates to a compressor bearing, e.g., a bearing for a screw compressor.
2. Description of the Prior Art
Heretofore, as a radial plain bearing for supporting a rotor shaft of a screw compressor, as is disclosed in Japanese Patent Laid-Open Publication No. 2005-69186, there has been used a dynamic pressure plain bearing having a fixed sliding surface, especially a cylindrical full journal bearing, because a high load is imposed on the bearing in a certain constant direction during operation of the compressor. In the full journal bearing, as shown in FIG. 8, in order to supply oil to a bearing surface 22 which supports a rotor shaft 21, an oil groove 23 is formed on the side opposite to the direction of a bearing load P and oil is supplied from the exterior to the oil groove 23 through an oil supply hole 24. Since the oil groove 23 is used also for cooling the rotor shaft 21, a circumferential length A of the oil groove 23 is set at a wide angle of about 120°.
In an oil-cooled screw compressor, the oil supply pressure is equal to the discharge pressure of the compressor, so that the internal pressure of the oil groove is also approximately equal to the discharge pressure. On the other hand, an ambient pressure of a bearing is approximately equal to the suction pressure of the compressor. Therefore, both a load P1 induced by normally acting compressed gas and a load P2 induced by the oil pressure in the oil groove act on a rotor shaft. In the case of a high pressure compressor, the oil supply pressure also becomes high and hence a load P2 of for example about 1.5 times as much as the load P1 acts on the rotor shaft. Consequently, there has been a case where the bearing cannot withstand and is damaged.
If the angle of the oil groove 23 is set small, the area of oil pressure acting on the rotor shaft 21 becomes smaller and it is possible to diminish the load P2, but there has been the problem that the rotor shaft 21 cannot be cooled and undergoes a thermal expansion, with consequent loss of a gap and damage of the bearing.